1. Field of the Invention
The invention relates to a device structure and the process thereof and more particularly to a device structure and the process thereof which forms a ring on the sensitive area of the sensor chip in order to bind to the sealant, and forms an opening in the ring.
2. Related Art
Lately, certain consumer electronic goods such as a watch manometer or a cell phone can be very successful by integrating a manometer therein. Therefore, based on the increase demand of the forgoing applications, how to provide a low cost manometer module and a small size of manometer module becomes a concern in this manometer module assembly business, since the pressure sensor is where the main cost of the assembly will be. According to the present technology, the design of a pressure sensor assembly is primarily following a two step process, where a preformed lead pin frame process is followed by an exterior cover process. The differences between those related patents involve the structure of the preformed lead frame, the location of the test pressure source conducting hole or the location of the reference atmosphere pressure hole. The prior patents, such as U.S. Pat. Nos. 5,852,320, 4,655,083, 5,465,626, 6,066,882, 4,563,697 and 5,209,120 are mainly focus on the use of a single unit process to perform the assembly of the relative pressure sensitive module. As to the structure of the preformed lead frame, they are mainly using a TO-can plastic frame with an outer lead metal. And regarding to the lead welding structure of the electric interface of the pressure sensitive module, there are two kinds of processes: one is through hole and the other is surface mount technology (SMT).
In addition, more and more pressure sensor modules are introducing a one dimensional batch process, where uses a bulk substrate with a matured one body mold to increase the throughput of the pressure module. The bulk substrate often is a printed electric board (PCB) or a lead-frame. Basically, the molding process in nature has an inherent property of mass production which has an advantage in cost reduction, so it is widely accepted by the major assembly manufacturers that it is an efficient process for cost down. However, in order to fulfill the special need when design a chip sensor of a pressure sensitive module, the sensor chip, the test pressure source conducting hole and the reference atmosphere pressure hole must to be processed or to be released before or after the molding process. There are three kinds of processes to do it. The first one is occupying the location of the via with a inserted bump mold in advance before the injection forming process of the molding is performed, and then after the mold is filled with the liquid plastic and becomes solid, the inserted object which is in the mold will be separated along with the mold removing process. So, the via hole will be formed naturally. The process is shown in U.S. Pat. No. 5,897,338.
Another process is so-called process to release method, which is using the etching process after the whole sensor module is molding and formed to etching out the material of the unnecessary part of the area which is designed for the hole till the sensor chip or the protection layer above is exposed. As a result, the via space for the sensor chip is released. The related patents can refer to U.S. Pat. No. 4,823,605 and the U.S. Pat. No. 6,379,988. FIG. 1A shows the micro-electro-mechanical pressure sensitive device 10 of the U.S. Pat. No. 6,379,988. In the figure, in order to protect the micro-sensor or the actuator above the micro-electro-mechanical sensor 11, before the molding process of the micro-electro-mechanical sensor 11, a sacrificed protection layer 13 will be in advance covered on the micro-electro-mechanical sensor 11 and will be embedded in the molding material 14 after the molding process. Consequently, there must be a window to be opened above the micro-sensor or the actuator 12. The window opening process is shown in FIG. 1B and FIG. 1C, where there are two different strong acids used for spray etching. In one process, a first pad 15 is formed on the molding material 14 to define the area to be etched. Then, a first strong acid 16 is sprayed for a certain amount of time to allow the molding material 14 which is exposed to the first strong acid 16 to be able to be removed to expose the sacrificed protection layer 13. After that, a second pad 17 is used to cover the first opening area of the molding material, and a second strong acid 18 is used for spray etching for a certain amount of time to remove the sacrificed protection layer 13. So the micro-sensor or the actuator 12 of the micro-electro-mechanical sensor device 11 will be released and exposed to the air.
The other process is a mix, which utilizes the two-step preformed lead frame process and the one-dimensional batch process. The exterior cover process is used to form the sensitive via hole of the sensor chip while the whole sensor module is formed by one body molding. That is, the sensor chip after formed by the one body molding process is binding to the saved space of the formed module and the exterior cover which has a saved via hole will then assemble to the sensor module body. The related patents are U.S. Pat. Nos. 6,927,482 and 6,401,545.
To summarize the forgoing processes, the single unit process method may have the throughput problem, which on the other hand may make a high cost preformed lead plastic substrate device even more costly. Therefore, from a view of upstream and downstream manufacturers, it is very difficult to reduce the overall cost of the assembly. Thus, a new package model is probably a possible and necessary way to solve this problem. In addition, the through hole and the metal lead frame processes need more foot print area than the regular base area of the manometer module, which will put a limitation to the reduction of the size of the whole module.